1. Field of the Invention
The present invention relates generally to an automatic power transmission for an automotive vehicle. More specifically, the invention relates to an automatic power transmission with a mechanism for establishing an under-drive speed ratio which is lower than a first speed ratio. Further particularly, the invention relates to a structure for rotatably supporting friction elements and control element in an under-drive mechanism.
2. Field of the Invention
An automatic power transmission with a subsidiary transmission unit has been disclosed in Japanese Patent First (unexamined) Publication (Tokkai) Showa 61-79068. The shown transmission includes a primary transmission unit and a subsidiary transmission unit. The subsidiary transmission has an additional planetary gear set which includes a ring gear supported on a subsidiary shaft and a pinion carrier receiving input force via the ring gear. A clutch drum is also provided for establishing engagement between the pinion carrier and a sun gear. The clutch drum includes a friction element engageable with the sun gear and another friction element for fixing or anchoring the sun gear onto a subsidiary transmission casing via the clutch drumm and an one-way clutch provided in parallel relationship with the friction elements.
The sun gear is supported on an output shaft via a pair of bearings. The clutch drum is integrally formed with the inner race of the one-way clutch and is supported on a support via a pair of bearings. In addition, a pair of end bearings are provided for centering the outer race of the one-way clutch. A spline member is separately formed from the sun gear, which spline member firmly engages with the spline section of the clutch drum.
With such construction, the pair of bearings becomes necessary for supporting the sun gear on the output shaft so as to prevent swaying of the sun gear and the drum support when the input force is active on the interengaging spline sections. Furthermore, since the long needle bearing cannot be used for supporting the sun gear because of high possibility of seizuring, a plurality of bearing becomes necessary.
Therefore, too many bearings employed in the subsidiary transmission may result in high friction for causing power loss. Furthermore, great number of parts makes the assembling process complicate and costful.